Vehicle headlamps are designed to project high intensity beams of light in prescribed patterns to illuminate certain portions of the road in front of the vehicle. Generally, vehicles are equipped with a first pair of headlamps, referred to as the "high beams", to illuminate the highway generally in front of the vehicle, and a second pair of headlamps, referred to as "low beams" which are directed downwardly in front of the vehicle and slightly to the right so as not to blind oncoming motorists.
In order to produce a desired illumination that maximizes visibility at night without producing excessive glare for oncoming motorists, the headlamps must be properly aimed and produce a particular light pattern. Standards for headlamp aiming and illumination patterns are prescribes by industrial groups, such as the Society of Automotive Engineers (SAE), and by governmental agencies. In general, different aiming and illumination pattern standards have been prescribed for different geographical areas, such as North America and Europe.
Various methods and apparatus for determining proper vehicle headlamp aim during vehicle manufacture, and after vehicle has been in use, are known. In general, these methods sense the light intensity across the headlamp light beam, compare the light intensity to prescribed standards, and provide an output which can be used to accurately adjust the headlamp.
One type of early method for aiming a vehicle headlamp is referred to as "hot spot" aiming, wherein location of the hot spot of the intensity pattern is compared with appropriate specifications to determine if the headlamp is properly aimed. A more recent approach to headlamp aiming, which was developed by the assignee of the present invention, is referred to as the "fractional balance" method, wherein relative intensities of different portions of the light beam are compared. Further, an even more recent method developed by the assignee of the present invention is referred to as "pattern framing" wherein a row and column of pixels having prescribed light intensities relative to the hot spot are determined, and the intersection of the row and column is compared with appropriate specifications to determine the accuracy of the aim. These methods are disclosed in detail in Irwin, U.S. Pat. No. 3,515,483; Hopkins, U.S. Pat. No. 4,948,249; and in co-pending application Ser. No. 07/964,599, filed Oct. 21, 1992, for "Headlamp Aiming Method Using Pattern Framing", respectively, all of which are owned by the assignee of the present invention.
Vehicle manufacturers typically provide standards for vehicles on the assembly line so that headlamp aiming can be accomplished relatively accurately and rapidly within the manufacturing facility. For example, the manufacturers provide specifications indicating the supposed distance from the floor of the manufacturing plant or facility to the center of the headlamp. When the headlamp is to be aimed, a headlamp aiming device is positioned generally in front of the vehicle at the particular manufacturer's suggested height, and an appropriate aiming method is used. Properly positioning the headlamp aiming device in front of the vehicle is important because a poorly positioned headlamp aiming device can result in incorrect aiming of the headlamp.
However, as should be apparent, various factors can influence the height of the vehicle in the manufacturing facility, and therefore inadvertently change the height of the vehicle headlamp with respect to the floor surface. Such deviations can materially affect the quality of the aiming process and provide an incorrectly aimed headlamp. For example, the tires of the vehicle could be over or under-inflated, customizing or modifications of the vehicle could add extra weight to the vehicle and therefore lower the height of a vehicle, or different types of headlamps could be periodically substituted without appropriate corrections being made to the height of the headlight aiming device. Accordingly, such factors could influence the actual level of the vehicle headlamp above the floor of the manufacturing facility, and therefore affect the quality of the aim. Moreover, the manufacturer-provided specifications can be ineffective for accurately positioning the headlamp aiming device at locations remote from the manufacturing facility, such as at a service station or repair facility.
To facilitate positioning the headlamp aiming device correctly in front of the automobile in the manufacturing facility, or in a remote field location, such that the headlamp can be properly aimed using an appropriate aiming method, certain centering devices have been developed. These centering devices position the headlight aiming device centrally in front of the headlamp to some degree of accuracy. These devices can be used in conjunction with the manufacturer's specifications to confirm the location of the headlamp above the surface of the floor, or can be used independently in a remote location such as a service station or repair facility.
For example, Irwin '483 uses a retractable arm connected to the aiming device for generally positioning the lens in the device centrally in front of the headlamp.
A similar device is shown in co-pending application No. 07/964,599, for "Headlamp Aiming Method Using Pattern Framing". According to this invention, a mechanical probe is used for initially orienting a lens or focusing aperture relative to the headlamp. The probe is pivotally connected to the housing of the lens or aperture and can be moved away from the lens or aperture after orientation of the headlamp.
Finally, Hopkins '249 shows four discrete light intensity sensors (e.g., photovoltaic cells or photoconductors) disposed around the periphery of the lens for centering the headlamp relative to the lens. The light intensity sensors provide an output corresponding to the light intensity at each sensor. The relative positions of the headlamp and lens may be adjusted so that the relative amounts of light captured by each sensor, as indicated by its electrical response, are balanced according to a centering standard.
While the above-described devices provide a certain amount of accuracy and consistency in centering the aiming device in front of the headlamp, there is a demand for an improved centering means for centering the headlamp relative to the lens (or aperture) in the aiming device so that accurate aiming of the headlamp can be accomplished.